Firmware sentinel bump to LF6.1.55_2.2.0

[angolini]

• Rename firmware-sentinel to firmware-ele-imx
• Update firmware-nxp-wifi to align to the NXP BSP LF6.1.55_2.2.0 (merge the bbappend content into the recipe)
• imx-boot-firmware-files Update 8.18 -> 8.20
• firmware-imx: Update 8.18 -> 8.20
• firmware-imx-8: Update 8.18 -> 8.22

For the rename firmware-sentinel, I created only one commit for the recipe and for the imx-base change. Please, let me know if it's preferable to have it split in 2.

Testing

I don't have access to the machine; this update focuses on imx93 and some imx8mm details. I can upload the image if needed.

I built each recipe, and then I built the core-image-base. The build works.

[angolini]

@thochstein, could you please take a look at this PR? I think this might be a trick as there is a recipe rename, and mainly, I'm not sure if the COPYRIGHT is adequately set.

Thanks in advance.